Coaxial crystal detector and line



June 19, 1951 J. P. LEIPHART 2,557,,122

COAXIAL CRYSTAL DETECTOR AND LINE TERMINATION DEVICE Filed Sept. 27,1945 2 Sheets-Sheet 1 Ila-L -INPUT J. PLUMER LEIPHART June 9 J.\P.LEIPHARTI 2,557,122

COAXIAL CRYSTAL DETECTOR AND LINE TERMINATION DEVICE Filed Sept. 27,1945 2 Sheets-Sheet 2 J. PLUMER LEIPHART @WLW Patented June 19, 1951UNITED STATES PTENT OFFICE COAXIAL CRYSTAL DETECTOR AND LINE TERMINATIONDEVICE amended April 30, 1928; 370 0. G. 757) This invention relatesbroadly to coaxial lines as used for the transmission of radio-frequencyenergy and, more particularly, to a coaxial device for simultaneouslyterminating such a coaxial 2 Since radio-frequency apparatus frequentlyfor its activation requires that the input thereto be of a rectified ordirect-current (D. C.) character, it is accordingly another object ofthis invenline' in a desired impedance and rectifying the 5 tion toprovide coaxial terminal rectifying means radio-frequency outputthereof. operative to produce, for Whatever utilization In the practiceof those electrical arts that purpose and with reasonable accuracy overan contemplate the transmission of radio-frequency unusually wide rangeof operating frequencies, energy along a coaxial line, there frequentlysubstantially half-Wave rectification of the arises occasion to providea special termination radio-frequency voltage or current output from forsuch a coaxial line. This is commonly true, any coaxial line of givencross-sectional dimenfor example, when it is desired to connectextersions and characteristic impedance at any ternal metering ormeasuring apparatus thereto minal point thereof at which said rectifyingfor the purpose of measuring the voltage, current, means is utilized. orpower output of a radio frequency transmis- An important feature of thisinvention is that sion system. As is well known, however, unless itprovides a compact, coaxially-arranged termithe termination thuseffected is such as to prenal connecting and rectifying device by meanssent to the coaxial line an impedance substam of which radio-frequencymeasuring apparatus, tially equal to the characteristic impedance ofrequiring for its operation half-wave rectified the line, the observedmeasurements will be dis-- voltages or currents, may be operativelycontorted by fi C S a s from pedance mlsnected to any terminal pointalong a coaxial match, reflection, and standing Waves along thetransmission line of given cross-sectional dimencoaxial line. It isknown also that when altersions and characteristic impedance; and bynatin'g currents are caused to circulate through means of which also anyinaccuracies arising a network of co ect lead-S at y igh fre fromimpedance mismatch, reflection, and standquencies, particularlyfrequencies in excess of ing Waves, or from lead inductances and stray100 megacycles per second, the effects of lead iniring capacitances, maybe minimized or elimiductances and stray Wiring capao tances ca natedentirely, over an unusually wide range of sume such serious proportionsas to necessitate erating frequencies, when measuring radiospecialprovision for neutralizing them. For frequency Voltages, currents, powert Said these reasons, therefore, such common methods terminal point ofconnecting r eq y metering p In accordance with this invention, thedevice tus to a coaxial transmission line as y means of comprises aparallel network, coaxially mounted Wire leads have been found tointroduce serious d arranged adaptably t engage coaxial errors at frequec e pp the llltla-hightransmission line terminal connector, and confrque cy range, unless Step5 are token to sisting of a resistance inparallel with a capacipe sate therefor b the insertion of some tor andwith a unidirectional rectifying crystal, justable impedance-matchingdevice, as is known th capacitor and -m1 being connected in in the art.However, the use of such prior imseries, pedanc -m hi devices generallyhas the In one preferred embodiment of the invention, advantage thattheir tun tends to Vary the resistance comprises a non-inductivedisksiderably Wit e pfi fi frequency; so that shaped resistor having acentral hole thereto provide a fixed-tuned coaxial typ telminatthrough,contiguous with which and contiguous ing dev e, p e of Operation CV61 aWide range also with the outer periphery of one side of the of ultra-higfrequencies, WOuld be of advantage disk are provided concentric annularterminal in the art. means adaptable to engage the inner and outer It isaccordingly an object of this invention to conductors of a coaxialreceptacle, respectively. provide a simple and compact coaxial terminat-The resistor, capacitor, and crystal each are aring device by means ofwhich any coaxial transranged to be separately replaceable, and topromission line, of given cross-sectional dimensions vide for thiscontingency a separable coaxial and characteristic impedance andcarrying radiomounting is employed in which they are enclosed. frequencyenergy at frequencies ranging from Said mounting comprises essentially:a coaxial very low to beyond the ultra-high-irequency connector; acoaxial housing so constructed and band, may be terminated insubstantially its arranged as to accommodate the aforesaidparcharacteristic impedance at any terminal point allel network andcomplete the requisite electrialong such line at which the device may beinsorted.

cal connections thereof, and to provide a coaxial receptacle for saidcoaxial connector such that the outer and inner conductors thereof maybe electrically connected across the aforesaid disk 7 resistor;supporting structure for said coaxial mounting; means for makingexternal electrical connections thereto across the said capacitor; andmeans for attaching said coaxial connector at one end to said coaxialreceptacle and at the other end to a coaxial transmission line terminalconnector so as to connect the said coaxial line electrically across theaforesaid parallel network.

The foregoing, together with other objects, advantages, and features ofthe invention, may be understood more fully from the followingdescription of one preferred embodiment thereof when taken inconjunction with the accompanying drawings, wherein a crystal voltmeterarrangement utilizing the invention is illustrated by way of exampleonly, and in which:

Fig. l is a front elevational View of a preferred embodiment of theinvention, with rectifying crystal cartridge removed to show thearrangement of certain of the contact fingers;

Fig. 2 is a longitudinal section of the device illustrated in Fig. 1,taken substantially along the line 2-2 of Fig. 1, but with the crystalcartridge shown housed therein in its proper operating position;

Fig. 3 is a front elevational view, on considerably enlarged scale,showing a typical circular dag disk resistor such as employed in theFig. 1 device; 7 Fig. 4 is a fragmentary sectional View. of the I Fig. 3resistor, still further enlarged, taken substantially alongthe line 44of Fig. 3 and showing details of the structure thereof;

Fig. 5 is a schematic diagram of the electrical circuit and associatedcomponents of a crystal voltmeter arrangement utilizing the device shownin Figs. 1 and 2; and

Fig. 6 is a side elevational view of the rectifying crystal cartridge.

Referring now to the drawings, there is illustrated therein onepractical embodiment of the invention, designed for use in conjunctionwith a suitably sensitive meter to measure radio-frequency voltages ofrelatively small magnitude (such as the output voltages from anultra-highfrequency signal generator) along a standard 50- ohm coaxialtransmission line.

As illustrated in Figs. 1 and 2, reference numeral II] generallydesignates the hollow coaxial housing wherein there is mounted aninsertible unidirectional rectifier means: specifically, the steppedcartridge-type crystal II (see Fig. 6), of which one example known tothe art is the socalled Western Electric type 1N21 crystal. The housingIt is shown as comprising a flat annular metal disk-like front part I2and a separable coaxial rear part I3; the latter being formed by thehollow metallic cylindrical member I4 and the coaxial connector memberI5, coupled together by the metallic coupling ring I6. A flat circularflange I! is provided at one end of the member I4. Disposed between thefront disk I2 and the flange H of the separable rear part I8 is anannular wafer-like member I8 of mica or other suitable dielectricmaterial, which together with the disk I2 and the flange I1 forms acapacitor, the purpose of which will become more apparent from thesubsequent description of the device. Metal screws I9 secure the membersI2, I1 and I8 together, each of these screws being electricallyinsulated from the front disk I2 by means of an insulating sleeve 20 ofvulcanized hard rubber or other suitable insulating material, and beingscrew-threaded at their inner ends into the flange IT to provide goodelectrical connection therewith. The two lower screws I9 shown alsoserve to mount the rear part I3 of the housing Ill securely on (andconnect it electrically to) the metal supporting bracket M, which inturn is fixedly mounted on and electrically connected to the metal base23 by the screws 22.

The substantially half-wave rectified D. C. output of the device may beremoved by means of leads, as shown at 24 and 25, the lead 24 beingconnected to the front disk I2 by means of a short screw which issufiiciently short to penetrate only into disk I2. Output lead 25 formsthe ground return lead and is connected, in this illustrative example,to the base 23 by means of a screw 22' attached thereto at someconvenient point, such as shown in Fig. 2, the electrical circuit beingcompleted to the rear part I3 of the device by way of base 23, bracket2!, and the two lower screws I9.

thick and presents a capacitance of approximately 100 micromicrofarads.This wafer is provided with suitable marginal perforations and with acentral opening, for passage of the screws I9 and insertion of thecrystal cartridge II, respectively.

Both the front part I2 and the member I4 of the rear part I3 of themounting II] are axially perforated and recessed to permit the insertionof crystal cartridge II and provide coaxial cylindrical chambers 26 and27 espectively, of appropriate size and cross-sectional dimensions.

Annularly arranged metal fingers 28, which protrude outwardly andforwardly from the periphery of the central aperture in the front partI2 of the device, embrace and firmly grip the cylindrical flanged metalcap 29 of the crystal cartridge I I, thereby establishing goodelectrical conductive contact therewith. Similarly, the internalaxially-located and annularly-arranged metal fingers 30 perform asimilar function with reference to the cylindrical metal tip 3| of thecrystal cartridge I I. Fingers 30 project from and are integral with themetal plug 30, which forms the inner coaxial conductor of member IA. Theother end of the plug 30' is of reduced diameter and screw-threaded forattachment to the correspondingly hollowed and threaded centralconductor 32 of the coaxial connector I5. When plug 30 is screwed homethrough the central hole 33 of the disk-shaped, non-inductive resistor34 (which in this illustration is of the type known to the art ascircular dag), a firm contact is established between the central annularmetallic terminal 35 of resistor 34 (considerably wards the coaxialconnector member I5. The

connector member I5 is provided at one end with a circular flange 36which is engaged by the coupling nut I6, whereby a firm contact isestab;

lished with the end of the member I4. The member I4 is externallythreaded as indicated at 31 to receive said coupling nut i6, whereby theclamping and electrical connection of the circumferential annularmetallic terminal 38 of resistor 34 between the flange 36 and the end ofthe member I 4 is effected when the metallic coupling nut I 6 is screweddown tightly in place.

The input end of the central conductor 32 of coaxial connector I5 isshown in this particular illustration as being of a split-sleeveconstruction, having spaced fingers 50, while the outer conductor ofconnector I5 is externally threaded at its input end as indicated at 4I. This arrangement is designed to accommodate the common type ofcoaxial transmission line terminal connector (not shown) which includesa central axial metal prong and an external loosely-rotatable threadedsleeve (similar in operation to coupling nut I6) for seating connectionsfirmly. Other types of coaxial line terminal connectors may beaccommodated in similar fashion, as by alternatively constructing thecoaxial connector member I5 to include such a central axial prong and/orsuch an external threaded sleeve at its input end as may be necessary tomate the particular terminal connector being used with the coaxialtransmission linein fact, in practice a set of various types ofinterchangeable connectors l5 might profitably be constructed, to coverthe various possibilities. Also, while connector member I5 isillustrated in Fig. 2 as being filled with solid polystyrene 45, this ispurely for purposes of insulation and support and is not vital to theaction of the device. Any suitable dielectric material can be used forthe filling 45, or it can be eliminated entirely.

Figs. 3 and 4 illustrate the construction of the circular dag resistor34, in which Fig. 3 is a front elevational view thereof at approximately6 times normal size, while Fig. l shows a further enlargedandconsiderably exaggerated fragmentary cross-section thereof taken alongthe line 44 of Fig. 3. In this illustrative example, the annular centralterminal 35 and circumferential annular terminal 38 each comprise flashcoatings of silver, approximately .010 inch thick, impressed on one faceof a circular backing disk 42 of Bakelite or other suitable insulatingmaterial. The non-inductive intermediate annular resistant section 43shown in Figs. 3 and 4 comprises a flash coating of carbon,approximately .001 inch thick, impressed on the same face of base 42throughout the area intervening between annular terminals 35 and 3B, andsufiicient to present an electrical resistance of the order of sixtyohms between said terminals. The resistor 34 also has a central hole 33of sufiicient diameter to just permit passage of the threaded portion ofplu 30, as illustrated in Fig. 2.

The equivalent circuit for the preferred model herein discussed is shownschematically in Fig. 5, with connections to the coaxial transmissionline terminal T and output meter M indicated by dotted lines, and.operates as follows to provide a substantially half-wave rectified D. C.output across terminals 26 and 22'. Radio-frequency impulses fromcoaxial transmission line T impressed at the input end of connector I5,as at points 40 and 4 I, effectively see the parallel networkcomprisingthe non-inductive circular dag resistor 34 across theseries-parallel combination of unidirectional rectifying crystal II inseries with radio-frequency by-pass capacitor I 8 and meter M inparallel. For an impressed impulse of one polarity (which for purposesof discussion we shall call positive) the D. C. resistance RX ofiered bycrystal II is quite low (of the order of 200 to 300 ohms in a practicalcase of the Type 1N21 crystal cited), whereas for impressed impulses ofthe opposite (or negative) polarity its D. C. resistance Rx is very high(probably of the order of several thousand ohms) Thus the magnitudes ofthe currents and resultant voltage drops across the various elements ofthe parallel network will differ widely, according as they arise fromimpulses of positive or negative polarity impressed at input points 40and. 4|. They also will vary with frequency, but to a much less extent.In this illustration, the positive direction of current fiow through thecrystal I I is assumed to be from tip 3| to cap 29, as is commonly thecase in practice.

It may help to clarify the discussion if we assign definite values, ofan order of magnitude we might expect to meet in a practicalapplication, to certain of the variables involved. Accordingly, let usassume, in addition to the already-mentioned 50-ohm characteristicimpedance of the coaxial transmission line, that the actual frequency 7is 1000 megacycles per second, that the resistances offered by crystalII at that frequency are Rx=250 ohms in the positive direction andRX=2500 ohms in the negative direction, that the magnitudes ofresistance 34 and capacitance I8 are R=62.5 ohms and C=l00micromicrofarads, respectively, and that the resistance Rm of meter M,looking in from terminals 26 and 22', is ohms. Then the magnitude of thereactance [X01 offered by capacitor I3 at frequency f will be, employingthe usual formula, quite small:

, far as any negative radio-frequency impulses that might slip throughcrystal 1 I are concerned, the magnitude of the combined impedance ofmeter M and capacitor I 8 working out in the example cited to beapproximately 1.07 oh ms at frequency 5'. Furthermore, since themagnitude R of resistance 3 is only 62.5 ohms, whereas the combinedimpedance of the other branches of the parallel network will beapproximately 2500 ohms in the negative direction, it is clear that morethan 97% of all negative radio-frequency impulses impressed at inputpoints 1 3 and ll in this illustrative example will be by-passed throughresistor 34. Also, the combined impedance of the parallel network in thenegative direction will have a magnitude of approximately 61 ohms.

On the other hand, positive impulses impressed at the input points ii)and 48 will effectively see the 50-ohm characteristic impedance of thecoaxial line, since the magnitude of the combined impedance [Z] of theparallel network will then be approximately:

Thus, the impedance of the coaxial line will be perfectly matched forall positive impulses, and nearly so for all negative impulses, therebyvirtually eliminating the undesirable effects of impedance mismatch,reflection, or standing waves that so frequently arise when terminalconnections are made to a coaxial transmission line.

Furthermore, it is evident that the current flowing through crystal H inthe positive direction will be substantial, being about one-fifth of thetotal such current furnished by the coaxial line. Hence, in spite of theshunting efiect of capacitor i8, adequate half-wave rectified D. 0.current will reach meter M to actuate a sensitive movement. For example,if the magnitude of the radio frequency voltage across input points 49and 4! in the foregoing illustration is assumed to be two volts, acurrent of the order of 40 milliamperes will fiowacross the 50-ohmparallel network in the positive, direction, of which approximatelyone-fifth, or 8 milliamperes, will pass through crystal 2 I.Approximately 100 of the 8 milliamperes, or 80 microamperes of half-waverectified D. C. current, will then flow through meter M, which is morethan required by, say, a 50-microampere movement. Also, since thecurrent in leads 24 and 25 will be essentially D. C. in character, theefiects of lead inductance and stray capacitance introduced by suchleads will be negligible.

The device as illustrated and discussed herein is suitable forconnection to any terminal T along any50-ohm coaxial transmission lineof given cross-sectional dimensions. It is to be noted, however, thatthe invention and the principles involved are not limited in theirpractical application to 50-ohm coaxial lines of given dimensions, norto voltage measurements. For example, by properly choosing the depth ofthe flash carbon coating 43, resistances 34 can be constructed ofsufficient range of magnitude R. to make it possible to present, incombination with the other elements of the parallel'network, a combinedinput impedance of any magnitude likely to be desired in practice.Coaxial transmission lines of different cross-sectional dimensions wouldsimply require that correspondingly different dimensions be adopted inthe construction of the coaxial elements of the device. It is alsoevident that meter M can be calibrated in terms of the known impedanceof the parallel network to read voltages, currents, or power.Furthermore, terminals 25 and 22 can be left open if for any reason itis desired merely to terminate the coaxial line (either in approximatelyits own characteristic impedance or in a different impedance) withoutusing the rectified output; or any other device requiring for itsoperation substantially half-wave rectified D. C. currents or voltagesmay be connected to said terminals.

The eifective frequency range of the device is determined chiefly by thereactance lXc! of capacitor it, since its magnitude varies markedly withfrequency, and to a lesser extent by probable coincident variations inthe magnitude of the resistance Rx of crystal H in the positivedirection. Considerably larger magnitudes C of by-pass capacitance itwill be required in order properly to shunt meter M at low radiofrequencies; while marked variations in the magnitude of Ex will requireofisetting changes in the magnitude R of resistance 34. By so choosingthe values as to strike an average for a particular band of frequencies,measurements ,of considerable accuracy :can be obtained over that band,the accuracy improving as the Width of the operating band of frequenciesis cut down. A rough working model, constructed approximately asdescribed herein, was found to give voltage readings accurate to within10% over the wide frequency range of 10 kilocycles to 1000 megacyclesper second.

The efiective voltage or current range of the device depends at the lowend largely on the sensitivity of the meter M used therewith, and at thehigh end on the burn-out point of the crystal H. The above-mentionedworking model was found to read down to .01 volt and up to at least 2volts.

It remains merely to point out that the device is not limited to the useof type 1N21 crystalsany type of unidirectional rectiiying crystal llhaving a suitably high back-to-iront resistance ratio and mounted in ametal-ended cartridge may be employed, provided that the coaxial crystalhousing l0, including fingers 23 and 30, is

constructed to fit it.

It will be obvious to those skilled in the art that further changes ormodifications may be made in the preferred embodiment of the inventionherein described without departing from the spirit thereof, and it is tobe distinctly understood, thereiore, that no limitations are intendedother than are imposed by the scope of the appended claim as limited bythe prior art.

The invention described herein may be manu iactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

What is claimed is:

An output termination for a coaxial line of'the internal conductor andsheath type comprising a coaxial coupler for receiving the end of theline and having internal and external conductors terminating in the sameplane, a flat annular resistor abutting in said'plane against theconductors to terminate the coaxial line and coupler with the desiredimpedance, a central cavity member in electric contact with the outerportion of the resistor and opposite the external coupler conductor, acrystal rectifierunit in the cavity, wholly outside the coaxial coupler,and spaced from the resistor, a conductor member connecting the crystalunit to the center of the resistor and the internal coupler conductor,and a conductive cap member contacting the crystal unit andcapacitatively coupled to the cavity member, the cap and cavity membersconstituting output electrodes for the line.

J. PLUMIER LEIPHART.

REFERENCES CITED 7 The following references are of record in the file ofthis patent:

UNITED STATES PATENTS 2,498,335 Hunt Feb. 21, 1950

